[PATCH 2/2] serial: 8250: Request full 16550A feature probing for OxSemi PCIe devices

[Maciej W. Rozycki]

Oxford Semiconductor PCIe (Tornado) 950 serial port devices need to 
operate in the enhanced mode via the EFR register for the Divide-by-M 
N/8 baud rate generator prescaler to be used in their native UART mode.  
Otherwise the prescaler is fixed at 1 causing grossly incorrect baud 
rates to be programmed.

Accessing the EFR register requires 16550A features to have been probed 
for, so request this to happen regardless of SERIAL_8250_16550A_VARIANTS 
by setting UPF_FULL_PROBE in port flags.

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
Reported-by: Anders Blomdell <anders.blomdell@xxxxxxxxxxxxxx>
Fixes: 366f6c955d4d ("serial: 8250: Add proper clock handling for OxSemi PCIe devices")
Cc: stable@xxxxxxxxxxxxxxx # v5.19+
---
 drivers/tty/serial/8250/8250_pci.c |    5 +++++
 1 file changed, 5 insertions(+)

linux-serial-8250-oxsemi-efr.diff
Index: linux-macro/drivers/tty/serial/8250/8250_pci.c
===================================================================
--- linux-macro.orig/drivers/tty/serial/8250/8250_pci.c
+++ linux-macro/drivers/tty/serial/8250/8250_pci.c
@@ -1232,6 +1232,10 @@ static void pci_oxsemi_tornado_set_mctrl
 	serial8250_do_set_mctrl(port, mctrl);
 }
 
+/*
+ * We require EFR features for clock programming, so set UPF_FULL_PROBE
+ * for full probing regardless of CONFIG_SERIAL_8250_16550A_VARIANTS setting.
+ */
 static int pci_oxsemi_tornado_setup(struct serial_private *priv,
 				    const struct pciserial_board *board,
 				    struct uart_8250_port *up, int idx)
@@ -1239,6 +1243,7 @@ static int pci_oxsemi_tornado_setup(stru
 	struct pci_dev *dev = priv->dev;
 
 	if (pci_oxsemi_tornado_p(dev)) {
+		up->port.flags |= UPF_FULL_PROBE;
 		up->port.get_divisor = pci_oxsemi_tornado_get_divisor;
 		up->port.set_divisor = pci_oxsemi_tornado_set_divisor;
 		up->port.set_mctrl = pci_oxsemi_tornado_set_mctrl;